Producers, suppliers, and consumers of electrical power rely on energy meters to monitor power consumption and quality for numerous purposes, including billing and revenue calculations, power distribution management, and process management. Traditionally, the primary means of measuring power consumption was an electro-mechanical power meter. A number of other types of meters and equipment measured other parameters of power generation, distribution, usage, and quality. As technology has improved, intelligent electronic devices (IEDs), such as digital power and energy meters, Programmable Logic Controllers (PLCs), electronically-controlled Remote Terminal Units (RTUs), protective relays, fault recorders, and the like, have slowly replaced their electro-mechanical and analog counterparts. The shift to IEDs from analog and electro-mechanical devices provides a vast array of advantages, including improvements in measurement accuracy (e.g., voltage, current, power consumption, power quality, etc.) and system control (e.g., allowing a meter to trip a relay or circuit breaker).
The voltages, currents, and frequencies employed in the various electrical systems that utilize IEDs vary widely from region to region (e.g., the United States and Europe), from application to application (e.g., industrial or residential), and across various parts of a power distribution system (e.g., generation, transmission, delivery, etc.). For example, power may be generated at one voltage (e.g., 30,000 V), but transmitted at another, much higher voltage (e.g., 110,000 V), to minimize heat-related power losses related to large electrical current in the transmission lines. Additionally, a series of power sub-stations transforms the voltages employed for transmitting power, to bring the voltage down to the level at which it is distributed to customers (e.g., 220 V). Industrial power consumers in one region may receive power at one voltage (e.g., 480 V), while residential consumers in the same region receive power at a second voltage (e.g., 120 V). Residential consumers in one region may receive power at one voltage and frequency (e.g., 120 V at 60 Hz in the United States) while similar consumers in another region may receive power at a different voltage and frequency (e.g., 230 V at 50 Hz in Europe).
Power measurements typically occur at a few industry-standard voltages and frequencies. Higher operating voltages and currents are reduced to a few standard current ranges, so that the higher operating voltages and currents can be measured by meters designed to measure within those voltage and current ranges (e.g., 120 V, 208 V, 220 V, 277 V, 347 V, and 690 V). However, the disparity in the voltages, currents, and frequencies employed, not withstanding the relatively few standard ranges in which measurements are taken, generally necessitates that different IEDs be purchased for different input ranges, in order to comply with the various standards which the IEDs must meet. For example, a digital power and energy meter designed to measure power consumption and quality at an industrial facility may be inoperable or inaccurate—failing to meet industry requirements for the particular application—if employed at a power generation facility.
Thus, to comply with the requirements for accuracy among the multiple standards adhered to across industries and geographical regions, manufacturers of IEDs commonly configure and sell multiple “options” for each model of meter, where each of the options includes a voltage and current level that the purchaser expects the meter to measure. The meters are thereafter calibrated to meet the required standards. For example, one standard requires that energy calculations be accurate to within 0.2%. While many meters are calibrated to achieve an error of no more than 0.2% for one range of input signal levels (e.g., 120 V or 69 V), measuring a different range of signal levels requires recalibration to achieve the desired accuracy. This requirement is often necessary because part-to-part variations in the meter design, and offsets and/or phase shifts in sensor and/or input networks, have varying effects at different signal levels.